If you use a version of Emacs prior to 24 that doesn't include
package.el, you can get it from http://bit.ly/pkg-el23. If you have an
older package.el installed from tromey.com, you should upgrade in
order to support installation from multiple sources.

Of course, it's possible to just place it on your load-path and
require it as well if you don't mind missing out on
byte-compilation and autoloads.

Paredit

Using clojure-mode with paredit is highly recommended. It is also
available using package.el from the above archive.